1. Technical Field
The disclosure relates to a cylinder head which can be connected at an assembly end side, or combustion chamber side, to a cylinder block, having at least two cylinders arranged along the longitudinal axis of the cylinder head, with each cylinder having at least one exhaust port for discharging the exhaust gases, which exhaust port is adjoined by an exhaust duct, and the exhaust ducts of at least two cylinders merge to form an overall exhaust duct within the cylinder head, so as to form at least one integrated exhaust manifold. At least one oil return passage is arranged on the side of the integrated exhaust manifold which faces away from the at least two cylinders, and at least one surface which is provided on that side of the cylinder head which is situated opposite the assembly end side, which surface delimits the cylinder head in the outward direction and serves for collecting engine oil and conducting said engine oil into the at least one oil return passage, with the at least one surface extending along the longitudinal axis of the cylinder head.
The disclosure also relates to the use of a cylinder head of said type for an internal combustion engine.
Within the context of the present disclosure, the expression “internal combustion engine” encompasses diesel engines, spark-ignition engines and any other suitable engines in which the combustion involves the working fluid.
2. Background Art
Internal combustion engines have a cylinder block and a cylinder head which can be or are connected to one another to form the combustion chambers. The individual components will be discussed briefly below.
To hold the pistons or the cylinder liners, the cylinder block has a corresponding number of cylinder bores. The piston of each cylinder of an internal combustion engine is guided in an axially movable manner in a cylinder liner and, together with the cylinder liner and the cylinder head, delimits the combustion chamber of a cylinder. The piston crown forms a part of the combustion chamber, and together with the piston rings, seals off the combustion chamber from the cylinder block or the crankcase to limit gases from the combustion chamber passing into the crankcase and to limit oil passing from the crankcase into the combustion chamber.
The piston serves to transmit the gas forces generated by the combustion to the crankshaft. For this purpose, the piston is articulatedly connected by a piston pin to a connecting rod, which in turn is movably mounted on the crankshaft.
The crankshaft, which is mounted in the crankcase, absorbs the connecting rod forces, which are composed of the gas forces as a result of the combustion of fuel and air in the combustion chamber and the mass forces as a result of the non-uniform movement of the engine parts. The reciprocating motion of the pistons is transformed into rotational motion of the crankshaft. The crankshaft transmits the torque to the drivetrain. A part of the energy transmitted to the crankshaft is used for driving auxiliary units such as the oil pump and the alternator, or serves for driving the camshaft for actuating the valve drive.
The crankcase is generally of modular, often two-part design. The cylinder block, which serves as the upper crankcase half, is supplemented by an oil pan which serves as a lower crankcase half. To hold the oil pan, the cylinder block has a flange surface. In general, to seal off the crankcase with respect to the environment, a seal is provided in or on the flange surface.
To hold and mount the crankshaft, at least two bearings are provided in the crankcase, which bearings are generally of two-part design and comprise in each case one bearing saddle and one bearing cover which can be connected to the bearing saddle. The crankshaft is mounted in the region of the crankshaft journals which are arranged spaced apart from one another along the crankshaft axis and are generally formed as thickened shaft extensions. Here, bearing covers and bearing saddles may be formed as separate components or in one piece with the crankcase, that is to say the crankcase halves. Bearing shells may be arranged as intermediate elements between the crankshaft and the bearings.
In the assembled state, each bearing saddle is connected to the corresponding bearing cover. In each case one bearing saddle and one bearing cover—if appropriate in interaction with bearing shells as intermediate elements—form a bore for holding a crankshaft journal. The bores are conventionally supplied with engine oil, that is to say lubricating oil, such that a load-bearing lubricating film is ideally formed between the inner surface of each bore and the associated crankshaft journal as the crankshaft rotates—similarly to a plain bearing.
To supply the bearings with oil, a pump for feeding engine oil to the at least two bearings is provided, with the pump supplying engine oil originating from the oil pan via a supply line to a main oil gallery, from which ducts lead to the at least two bearings. The supply line leads from the pump through the cylinder block to the main oil gallery. To form the so-called main oil gallery, a main supply duct is often provided which is aligned along the longitudinal axis of the crankshaft. The main supply duct may be arranged above or below the crankshaft in the crankcase or else integrated into the crankshaft.
As well as forming the combustion chambers, the cylinder head conventionally also serves to hold the valve drive. To control the exchange of gases, an internal combustion engine requires control elements and actuating devices for actuating the control elements. The valve actuating mechanism required for the movement of the valves, including the valves themselves, is referred to as the valve drive. It is the task of the valves driven by a valve drive to open and close the intake and exhaust ports of the cylinders to allow fresh air or mixture to be inducted into the combustion chambers and exhaust gases to be expelled from the combustion chambers.
One example of a valve actuating device includes inter alia at least one camshaft, on which a multiplicity of cams is arranged.
Overhead camshafts are conventionally mounted in the cylinder head, with the camshaft being held by a so-called camshaft holder which is provided on that side of the cylinder head which is situated opposite the assembly end side.
Like the crankshaft, the camshaft or the camshaft bearings is also supplied with oil. The description above with regard to the crankshaft bearing arrangement apply analogously, with the use of bearing shells as intermediate elements often being dispensed with, or with the bearings being designed, if appropriate, as rolling bearings.
To supply the camshaft holder with lubricating oil, a supply duct is provided that may branch off from the main oil gallery extending through the cylinder block and, in the case of overhead camshafts, extending into the cylinder head.
To vary the position of the camshaft in relation to the crankshaft for the purpose of adjusting the control times of the valves, use is often made of camshaft adjusters. In some engines, the position of the camshaft relative to the crankshaft is varied by a rotation of the camshaft. The variation of the control times is one measure for reducing the fuel consumption of an internal combustion engine. Camshaft adjusters are often hydraulically actuated and must likewise be supplied with engine oil.
The oil under pressure supplied to the camshaft and the variable camshaft timing (VCT) system leaks out through small orifices into the cylinder head. Once the oil is in the cylinder head, it is no longer under pressure, but pools in the cylinder head, of course, not on the side of cylinder head in which the combustion chamber is provided. Under the force of gravity, engine oil, drains through oil return passages through the cylinder head and block to the oil pan to thereby close the oil circuit of the internal combustion engine.
To collect the oil dripping from the camshaft and VCT a surface is provided on the side of the cylinder head situated opposite the combustion chamber side. The which surface delimits the cylinder head in the outward direction, that is to say concomitantly forms the surface of the cylinder head, and extends—like the camshaft and the crankshaft—along the longitudinal axis of the cylinder head. According to the prior art, said surface is an open, narrow duct, that is to say a channel.
The friction in the bearings mentioned and described above, in particular the bearings of the crankshaft and the camshaft, and also the friction in the connecting rod bearings and the piston-liner interface, depends significantly on the viscosity of the oil. When the temperature of the oil is lower, the viscosity is greater, the friction is greater, and the fuel consumption of the engine is greater. By bringing the temperature of the oil to its operating temperature from a cold start condition, improves fuel efficiency as well as reducing engine out levels of regulated emissions.